In human and veterinary medicine, it is often necessary to remove or cut live bone, such as in the drilling of holes into the teeth or jawbone in dentistry, the cutting of jawbone in oral surgery and the cutting of the skull in neurosurgery. It is in such case highly desirable, and in many cases absolutely necessary, for the success of such an operation that the bone be not damaged because otherwise the healing of implants or the knitting of a cut bone is very difficult or even may not be possible.
Further, damage to such bone can be expected at relatively low temperatures. The highest temperature which the tooth or other bony substance will tolerate lies at approximately 50.degree. C.
It is known to dissipate frictional heat by conducting a cooling fluid, such as water of physiological saline solution, as close as possible to the place of heat formation. For this purpose, nozzles for the discharge of cooling fluid are usually arranged on dental hand or elbow pieces, which nozzles spray cooling fluid from outside onto the tool (drill, milling tool). This method achieves a good cooling of the tool, however, it is often not possible to withdraw the heat from the place of formation, namely where the cutting surfaces rub on the substance which is to be removed. This is particularly true if drilling is done in relatively deep holes or if mechanical obstacles prevent the access of the cooling fluid to the tool portion which is in engagement with the substance to be removed. Thus with the known method the heat removal is often only indirectly possible through the tool. However, this type of heat removal is often not sufficient to prevent an intolerable heating of tooth or bony substance because of the poor heat transfer from the substance into the tool.
A disadvantage of the method used so far consists also in that relatively large amounts of cooling media must be supplied in order to obtain an at least somewhat sufficient cooling. The discharge of large amounts of cooling fluid is often difficult, for example, when a tooth treatment is carried out with the patient in a lying position.
The basic purpose of the invention is to improve an apparatus of the type mentioned above in such a manner that cooling fluid can be fed directly to the place of the heat development including when work takes place at a place which is difficult of access, for example in a deep hole.
This purpose is attained according to the invention by providing the tool with a longitudinal channel which opens outwardly at the working end of the tool and causing the conduit to communicate with the longitudinal channel.
During use of apparatus so constructed, the cooling fluid is conducted through the longitudinal channel to the front end of the tool and immediately after its exiting from the tool contacts the substance to be cooled. This is also assured when drilling takes place in a deep hole or if mechanical obstacles exist which would not permit an effective cooling from the outside. The apparatus of the invention, due to the direct feeding of the cooling media to the place which is to be cooled, permits operation with only relatively small amounts of cooling media which reduces the discharge problems. Intolerable heating of bone substance or tooth substance can also be avoided if work is done relatively quickly, namely if a relatively large quantity of such substance is removed per time unit. Rapid working with the previously used methods was difficult because of an insufficient cooling. Repeated pauses were necessary to prevent an excessive heating and to repeatedly cool a deep hole at short intervals due to the fact that cooling fluid was injected only after the tool was withdrawn.
In addition, the drilling or milling apparatus is not only usable in dentistry, but may be used wherever live bone is removed or severed. The severing of jaw bones, for example in prognathic operations, in jaw surgery and severing of head bones in neurosurgery, throat, nose and ear cases are a few examples. It is desired, and in many cases also an absolute condition for success, that the bone tissue does not suffer heat damages, because otherwise it is very difficult or not at all possible to heal implantations or severed bone. With the inventive apparatus, it is possible not to exceed the highest temperature of approximately 50.degree. C., which the tooth or bone tissue will permit, not even during quick working.